The present invention relates to a process for preparing trans-.beta.-benzoylacrylic acid ester having the general formula (I): ##STR3## wherein R is an alkyl group or aralkyl group. The purpose of the present invention is to provide a process for preparing the compound (I) in an industrially advantageous manner, the compound (I) being an important intermediate compound for the production of the medicines and the perfumes.
Hitherto, the most commonly known method for synthesizing the ester has been the method by the dehydration reaction between carboxylic acid and alcohol. This method has been used for synthesizing .beta.-benzoylacrylic acid ester, for example, ethyl .beta.-benzoylacrylate. In case of the dehydration reaction between .beta.-benzoylacrylic acid and ethanol, though it has been reported that ethyl .beta.-benzoylacrylate is obtained with a good yield, geometrical isomerism, i.e. cis-form and trans-form, of the starting material and of the product as well as the concrete procedure have not been described [Nippon Kagakukaishi, 88, 224 (1967)]. On the contrary, other report describes that the product of the ethyl-esterification reaction of .beta.-benzoylacrylic acid with ethanol is hardly purified [J. Amer. Chem. Soc., 45, 222 (1923)], while another report describes that ethyl .beta.-benzoyl-.alpha.-ethoxypropionate was obtained in the usual ethyl-esterification reaction [Bull. Chem. Soc. Japan, 42, 1353 (1969)]. Therefore, the above-mentioned method for synthesizing .beta.-benzoylacrylic acid ester by the dehydration reaction between 8-benzoylacrylic acid and alcohol is not suited for the method for industrially effective production of .beta.-benzoylacrylic acid ester since it has various problems to be solved such as unclearness of geometric isomerism of the product, of a kind of the products and of a quantitative ratio of the products. Under such circumstances, several different methods for preparing trans-.beta.-benzoylacrylic acid ester have been studied by many research workers. For example, a method by the aldol condensation reaction between acetophenone and glyoxylic acid ester (Japanese Unexamined Patent Publication No. 192622/1982) and a method by halogenating .beta.-benzoylpropionic acid ester and then dehydrohalogenating the resultant [J. Amer. Chem. Soc., 45, 222 (1923)]have been proposed. However, these methods are also disadvantageous for an industrial application since, in the former method, the product is not easily produced and very expensive glyoxylic acid ester is employed and, in the latter method, the reaction is carried out in a multiple step including a preparation of .beta.-benzoylpropionic acid ester and the yield is low. Also a method by esterifying trans-.beta.-benzoylacrylic acid by means of dialkyl sulfate or halogenated alkyl is not suited for the industrial production since it has various drawbacks such as noxious reaction agent and liquid-waste treatment after the reaction.
In order to establish the industrial process for preparing trans-.beta.-benzoylacrylic acid ester endowed with excellent operatability, safety and economical advantage, the present inventors have studied a condition for predominantly producing trans-form of the ester and surpressing the by-product in the reaction between .beta.-benzoylacrylic acid and alcohol.
As the result of the continuous effort of the present inventors, now it has been found that in the esterification reaction of .beta.-benzoylacrylic acid having the formula (III): ##STR4## with the alcohol having the general formula (V): EQU ROH (V)
wherein R is as above, by the dehydration reaction, considerable amount of .beta.-benzoyl-.alpha.-alkoxypropionic acid ester having the general formula (II): ##STR5## wherein R is as above, is by-produced in addition to desired trans-.beta.-benzoylacrylic acid ester having the general formula (I): ##STR6## wherein R is as above, and that the by-product (II) can be easily converted into the desired compound (I) by the dealcoholization reaction in the presence of an acid catalyst.